Is it possible to test with Jest an old non-module JavaScript?

Question

Consider an old project (very common in my opinion):

static/
   js/
      file1.js
      file2.js
      ....
   index.html

---

index.html

...
<script type="text/javascript" src="js/file1.js"></script>
<script type="text/javascript" src="js/file2.js"></script>
...

file1.js:

// publicly exposed class/function
var Person = function(name, age) {
    this.name = name;
    this.age= age;
}
Person.prototype.getName = function() {
    return this.name + '(' + this.age   + ')'
}

file2.js:

// publicly exposed function
var createPerson = function(name) {
    return new Person(name);
}

The contents of file1.js and file2.js are just dummy for showing the problem.

Is it possible to write a test of the form?:

file2.test.js:

// require('./file2');
// require('./file2');
test('create', () => {
    let person = createPerson('Tester', 40);
    expect(person.getName()).toBe('Tester (40)');
});

I tried searching for babel plugins that transform window/global attached variables to module exports, tried also with the Jest 'setupFiles' config property. Maybe Jest is not ment for such cases, just want to not look for another test framework as I already use Jest for other modern modular apps.

If not how to test such old application JavaScript - I know I can use Jasmine or Mocha and run the tests in the browser, but would like this to happen in Node environment, so that it could be finally handled with CI for instance?

Answer 1

You will need to merge the scope of the files as part of the current context - e.g. by synchronously loading and dangerously evaling the sources into the current test file - making anything imported in such a manner available there for testing (including potential unexpected conflicts and side-effects - as you would in a non-modular global window context).

const script = (url) => {
    const { protocol } = new URL(url, 'file://');
    switch (protocol) {
        case 'file:':
            return require('fs').readFileSync(`${process.cwd()}/${url}`, 'UTF8');
        case 'http:':
        case 'https:':
            return String(require('child_process').execSync(`wget -O - -o /dev/null '${url}'`))
        default:
            throw new Error('unsupported protocol');
    }
};

eval(script('js/file1.js'));
eval(script('js/file2.js'));

// ... tests